This invention relates to a transfer-printing sheet separating system for an electrophotographic copying apparatus for separating from the photosensitive member a transfer-printing sheet fed by the sheet feeding device to the photosensitive member formed on its surface with a toner image to print the toner image on the transfer-printing sheet, and a method for effecting registration of the transfer-printing sheet with the toner image on the photosensitive member.
When the toner image on the surface of the photosensitive member is printed on the transfer-printing sheet, the transfer-printing sheet is electrostatically attracted to the surface of the photosensitive member, so that difficulties are encountered in separating the transfer-printing sheet from the surface of the photosensitive member after printing of the image is completed. Various proposals have hitherto been made to use various systems for separating the transfer-printing sheet from the surface of the photosensitive member.
In one method known in the art, pneumatic separation means is used for blowing air against the transfer-printing sheet to separate same from the photosensitive member. This method has a disadvantage in that since the toner image printed on the transfer-printing sheet is not fixed when the transfer-printing sheet is separated from the photosensitive member, the toner may be scattered by the stream of air blown against the sheet and adhere to the parts of the copying apparatus.
In another method known in the art, separating claws are slid between the photosensitive member and the transfer-printing sheet. In this method, the separating claws in the form of knife edges are maintained in contact with the surface of the rotating photosensitive member at all times, so that damage, in the form of parallel lines, tends to be caused to the surface of the photosensitive member. When the copying process is that of a negative/positive system, the duplicate or copy so produced will have dark lines thereon if the photosensitive member is damaged as aforesaid, thereby reducing the quality of the copy. Also, when the forward edges of the separating claws are deformed as by prolonged use, it would become impossible to separate the transfer-printing sheet from the photosensitive member satisfactorily.
In still another method of the prior art wherein the charge on the transfer-printing sheet is neutralized by AC corona discharge, the end of separating the transfer-printing sheet from the photosensitive member cannot be attained depending on the ambient conditions, such as temperature and humidity, the quality and thickness of the transfer-printing sheet, and other conditions.
In still another method known in the art, a belt or other separating member is positioned beforehand on one portion of the photosensitive member. This method has disadvantages. When the belt is of a stationary type, wear would be caused on the photosensitive member. Since the position of the belt is constant, the method can be used when the transfer-printing sheet is set in a position by using only one side as a reference, but cannot be used when setting of the transfer-printing sheet is effected by using the center of the photosensitive drum as a reference. In addition, the transfer-printing sheet of a large width could not be separated satisfactorily.
A system for drawing the transfer-printing sheet by vacuum has been proposed. This system requires means for creating vacuum, thereby increasing the size and cost of the copying apparatus.